Uniflow engine



E. W. SWARTWOUT.

UNIFLOW ENGINE.

APPLICATION FILED JUNE 3,1916.

Patented Sept. 13,1921.

3 SHEETSSHEET I.

11-110 m foz E. w. SWARTWOUT.

UNIFLOW ENGINE- v APPLICATION FILED JUNE S, 1916- 1,390,398, PatentedSept. 13,1921.

3 SHEETS-SHEET 2- gym/Z7 %a//ZZ/mmm Mm E-. W. SWARTWOUT.

UNIFLOW ENGINE.

APPLICATION men JUNE 3. 1916.

iivnnnzrr w.-swna'rwonr, or warm Prams,

NEW RK- UNI-FLQW NGINE.

" Application filed'i'une 3, 191 6, Serial No. 101,511.

' To all whom may concern:

. invented certain new and useful Improvements in Uniflow Engines, of which the following is a description.

Thisinvention relates to the provision of clearance means 1I1 uniflowsteam engines and other devices employing inlet valves disposed ad acent the ends of the cylinder for the inflow of the medium and exhaust ports disposed centrally of the cylinder and controlled by the piston for the outflow of the medium. 7 v 1 A principal advantage of engines of the uniflow type as particularlycompared with engines of the counterflow type, is the elimination of so-called initial condensation of the steam, that is to say, the avoidance of condensing of a portion of the steam into water, as it enters the cylinder and thereby decreasing the amount of heat available for performing useful work. Such advantageous condition ensues only during the period or periods of continuance of the operating conditions for which any particular uniflow engine is specifically designed, and in practical operation such particular con% ditions prevail for relatively short periods. The usual causes of. departure from thepar ticular operating conditions'for which, the unifiow engine is designed, are leakage or failur of the condenser partsand variations in term erature of the condenser cooling water, t ereby giving rise to a so called decrease of vacuum in the exhaust belt, whereby an increase in the pressure of the cylinder takes place when the exhaust is closed and a consequent increase of the final compressional pressure and in excess of the initial pressure of the steam. Such excessive fcompressional pressure causes overheating and possible rupture of the parts of the engine,

According to my invention, there isprovided clearance vmeans comprising a plurality of clearance chambers or'spaces adapted to be brought into effective communication with the interior of the cylinder and the proper clearance value or total effective clearance determined or regulated to attain the desired smooth working. Such determination or regulationeffects the preclusion Specification of Letters Patent.

' ance values, and

iatented sle t. 13, 1921'.

of a compression pressure in excess of the initial pressure and is attained by'meanswhich is operated or controlled independently of the maximum compressional pressure. Preferably, the communication of clearance chambers or spaceswiththe interior of the cylinder is controlled by 'or inresponse' to the exhaust pressure, whereby the variations in the exhaust pressure control the communication of the clearance chamber or chambers at a time in advance of the instantat which the [piston I reaches the region" of itslimiting position. The communic'ation of, any clearance chamber or space with the interior of the cylinder is usu-ally'opened or closed by a valve and such valve may 'beemployed as a valve for opening or closing'the communication of all the' clearance chambers orsp'aces in common,

As one preferredformof my invention, I I.

allude to the double acting steam e'nglne of the unifiow or central exhaust type provided with clearance means, preferably-disposed at both the head and the frame end ofithe cylinder, controlling the communication of each port with the clearance proper of the engine,

each having a port,'and a valve Preferablyjalso the casings of each such valves and'the clearance spaces'are by live steam. The clearance spaces may be (if-equal clearance value or of unequal clearin the latter case may be heated v arranged'progressively increasing, or progressively decreasing. It is convenient capacities to arrange the'clearance spaces at any end of the engine, in juxtaposed relation and to control the communication between the ports ofv the same and thefclearance proper by a single valveoperated in accordance with the object's ofthis invention.

initial pressure, i. 6., boiler pressure, 1s

"nengines' of the usual According to modern steam practice, the

maintained substantially constant, and the usual variation 1s encountered by changes in the exhaust or terminal pressure. Under these circumstances, my invention s particularly advantageous in controlling the I clearance spaces in response to variation in exhaust conditions, as by suitable means operated either directly or indirectly in connection with the exhaust. i

' It will be understood that my invention in maximum tion will be more fully set forth in the fol lowing detail description and accompanying drawmgs, in which-- F lgure 1 1s a dlagrammatic central sectional elevation showing a form of my invention applied to the head of a unifiow steam engine;

Fig. 2 is a side elevation, partly in vertical central section showing my invention applied to the frame end as well as the head of a double acting uniflow steam engine; and Figs. 3, 1, and 5 are detail diagrammatic views'showing the clearance valve in different positions.

Referring to Fig. 1, the piston 1 is represented in the cylinder 2 at its position of compression. The clearance proper is represented by the space 3 disposed between the head of the'piston 1 and the head 4 of the cylinder 2, the clearance proper 3 being exaggerated somewhat as shown in Fig. 1, for the sake of clearness.

At a suitable location as in the head 4 is arranged the port 5 adapted to afford communication of the clearance proper 3 with the clearance spaces.

In the particular form of my invention indicated in Fig. 1, the clearance spaces are constructed in the form of a main chamber 6 and supplemental chambers 7, 8, 9, controlled by the piston valve 10 disposed within the chamber 6. The piston valve 10 is provided with the forward packing ring 11 and the rearward packing ring 12 and with a passage-way portion 13 disposed intermediate the packing rings 11, 12. The.

passage means shown as one or more perforations 14; extending through the piston 10 afford communication between the portions of the chamber 6 on both sides of the piston 10. Such passage means results also in a valve which is balanced for all positions.

' The chamber 6 is designed in capacity to provide the additional clearance required when the exhaust is varied from condensing condition to exhausting into the atmosphere, or equivalent pressure. As the pressure varies from vacuum toward atmospheric pressure, the piston valve 10 is moved to successively bring into communication with l the clearance proper 3 of the cylinder 2 the chambers 7 8 and 9, in the order named; or

in the inverse order for the variation of the pressure from atmospheric'toward absolute vacuum. Upon varying the condition of exhausting in a condenser to exhausting into the atmosphere, the piston valve 10 is moved to the'position of fully opening the port 5 into communication with both portions of the chamber 6 on the twosides of piston valve 10, but not into communication with any of the clearance spaces 7 8, 9. Under 6 the condition of slight back pressure in the exhaust region, the piston valve 10 will be moved still farther to open the port of supplemental clearance space 7 into communication with the main clearance space 6, but excluding communication of the supplemental clearances 8,9. Under increased back pressures, the supplemental clearances 8, 9,

and further supplemental clearances if desired, will be progressively brought into effective communication with the clearance proper of the cylinder by similarly increased movement of the piston valve 10, as more fully set forth hereinafter, in relation to Figs. 3, 1 and 5. I

As one means for effecting these functions, I have shown the following described means automatically controlled in connection with the exhaust region of the engine.

The valve stem 18 of clearance valve 10 is shown controlled by the exhaust responsive means, comprising the differential piston 19 fixed to said valve stem 18 and within casing 20. Said differential piston 19 is formed of the head portion 21, made steam-tight with the inner surface of casing 20, and the rearward portion 22 of reduced cross-sectional area, affording the variable pressure space 23 and the pressurearea 2 1 shown as annu lar in contour. The reduced portion 22 is made steam-tight with the partition ring 25. In the position shown in ig. 1, the differential piston 19 and accordingly the clearance valve 10, are in their respective extreme positions, restricting the clearance value to the clearance proper of the cylinder. At this point, it will be noted that the cubic capacity of the port 5 and passage portion 13 of the clearance valve 10 enter into the value of the clearance proper of the cylinder. 7

The vacuum pressure controlleris'shown as a piston 26 mounted in the casing 27, I

plained more fully hereinafter. The lower port 32 is connected with the passage 34 leading to the rotary three-way valve 35.

Similarly the upper port 33 communicates through passage 36 with another valve space of said three-way valve 35. I

The passage 37 of the three-way valve 35 opens to the atmosphere. The piping 38 leads to the boiler.

On the stem 18 of the plunger valve 10 is also arranged means for counterbalancing the effectual force applied to said differential piston-19, comprising the weights (four shown), 40, 41, 42, 43, preferably of progressively increasing masses, normally resting' on seats 44 afforded by the frame 45, and each Weight provided'with an opening through which the stem 18 freely passes. The abutment 46 is fixed to frame 45 and the spring 47 is positioned between said abutment 46 and the collar 48, fixed tostem 18. The strength of spring 47, adjusted by any approved-means, is made suflicient to overcome the weight of and friction against the stem 18, difierential piston 19 and clearance piston 10, and move the collar 48 against weight 40. One such approved adjustment means is indicated inFigs. 1, 3, 4 and 5, showing the cup 46 of spring 47 adjusted by means of screws 46*.

The springs 49 are preferably employed to serve as buffers and to effect gradual increase in the counterbalancing function, to which end the springs 49 are positioned intermediate and have their end portions engaging the respective weights 40, 41, 42, 43.

In the positions of the vacuum piston 26 and the differential piston 19 as indicated in Fig. 1, the pressure applied to the vacuum piston 26 may be the minimum for the design of the particular engine shown, say twenty-six inches vacuum running with a condenser, in which case, the

differential piston 19 is at its extreme 'lowest' position and the piston valve '10 restricts the port 5 to limit the clearanceto the clearance proper of the cylinder. It will be noted that the three-way valve 35, controlled vacuum piston 26 through link 56 and valve arm 50, under these conditions effects the communication of' the passage 34 to atmosphere to cause the atmospheric pressure to be applied to the face 21 of differential piston 19, while the face 24 of reduced area is being subjected to boiler pressure, by reason of the passage 36 being brought by the three-way valve 35 into communication with the passa e 38 leading to the boiler. Upon increasec pressure atthe exhaust region, 2'. 6.,11I1d61' conditions of less vacuum, the vacuum piston 26 will be moved downwardly, causing the movable valve member of three-way valve 35 to be turned (counterclockwise as viewed in Fig. 1), until the passage '36 will be cut off from connection with the boiler and be brought later in communication with the atmosphere, while at the same time the passage 34 will be cut off from connection with the atmosphere and brought into communication with the passage 51 leading to the exhaustregion. Under these conditions, the differential piston 19 will rise under action of the spring 47 modified by the differential pressure on the differential pressure piston 19.

During such upward movement of the differential piston 19, the piston valve 10 is cylinder 3 with the port 54 of the first clear-jv ance' chamber 7 then to the stage, as indicated in Fig. 4, of effecting communication I if v of the port 5 with the interior of thecasing 6, serving as the main supplemental clearance chamber; then to the stage as indicated in Fig. 5 of effecting communication of the port 5 of the cylinder 3 with the main clearance chamber 6 and the first supplemental clearance chamber 7 then successively to the subsequent stages of efiecting communication through the port 5 of the clearance proper of the cylinder3 with the main clearance chamber 6,.the first supplemental clearance chamber 7, together with the additional supplemental chambers 8, 9, etc.

The collar 48 is brought in contact'with the lower most weight 40 as the piston valve 10 progresses toward its position corresponding to atmospheric exhaust, as is indicated in Fig. 5; at the stage of atmospheric exhaust, the piston valve 10Jhas been movedupwardly'to its extreme position of effecting communication of the clearance proper through the port 5 of the cylinder 3 with the main clearance chamber 6 and all the supplemental clearance chambers 7, 8, 9, etc. Further movement of the piston valve '10 will uncover the port 54 of clearance 7 to add the same as an effective clearance value to f the main clearance 6 and clearance proper as indicated in Fig. 5, at which stage the first weight 40 will have been fully liftedafrom its seat 44. Continuing such increased pressure at the exhaust region, the port 53 of clearance 8 and the port 52 of clearance 9' will be successively uncovered and brought into effective communication with the clearances previously brought into operation, includingthe clearance proper 3 and the main clearance 6.

The maximum clearance, it will be'observed, ensues when the exhaust pressure is the maximum for which the device is designed. Preferably the vacuum piston 26 is constructed and its spring 31'adjusted so. that under the conditions of the attaining of the degree of vacuum at which the maximum performance with a clearance value of the clearance proper of the device is obtainech the vaculm piston 26 assumes the positionindicated in Fig. 1; and under the condition of pressure in the exhaust region approaching more or less atmospheric pressure, the piston 26 will be moved to turn the threeway valve 35 sufficiently to cause a. pressure of substantially atmospheric pressure to be applied to the reduced pressure area 24 of differential piston 19 and the pressure Oif the exhaust region "to be applied to .the face 21 of said piston 19. As the pressure in the ex- 10 to effect the successive addition of the 'lar exhaust pressure,

supplemental clearance spaces 7, 8, 9. Reversing the change in pressure conditions assumed above, upon the change in the exhaust region from atmospheric pressure, or excess thereof, to full or partial vacuum, tl eexhaust piston 26 will. ultimately be moved and the three-way valve caused to rotate in the clockwise direction, and cause the exhaust pressure and ultimately the boiler pressure to force the differential piston 19 downwardly, and therewith permit the clearance valve 10 under the force of the weight of the weights 40, 11, 42, 13 to successively cut out the supplemental and main clearance chambers from effective communication with the clearance proper of the cylinder.

When my invention is applied to an engine, it is preferable to incase the main and supplemental clearance means to provide heating the same with the heated medium, as by the casing 55 connected by the passage 55 as indicated in Fig. 2 with the inlet steam passage of the engine. A indicated in Fig.

1, the head may be thinned at the region of location of the clearance means, to thereby increase the heat radiation between the interior of the cylinder and the interior of the casing surrounding the clearance means.

In Fig. 2, I have indicated an approved type of'uniflow engine provided with clearance means embodying my invention at the frame end as well as the head of the cylinder, said clearance means being each automatically controlled by the exhaust by a suitable arrangement such as has been described above in connection with F 1. The above described means when applied to a unifiow steam engine accordingly provides a clearance means which is increased in effective clearance value asthe exhaust pressure is in: creased, due to withdrawal of steam for heating or other purposes. By means of my invention, therefore, the pressure of the steam at the end of the compression stroke will be precluded from exhausting the initial pressure and is maintained substantially equal to the initial pressure, by adjustment of the clearance, in correspondence to each particuthereby maintaining the pressure curve of maximum efficiency for the particular engine in question.

When the engine is running continuously noncondensing or under atmospheric exhaust, the three-way valve 35 may be rendered inoperative by closing the stop valves 70, 71, 72, respectively in the passages 30, 51,

condition the differential piston 19 is operated directly by the action of the exhaust pressure through the passage 61 .andthe port 33 connected through vthe passages 36, G2 with the atmosphere. 7

rind when the engine is run continuously non-condensing or under other conditions, upon closing the indicated stop-valves 70,71, 72 respectively in the passages 30, 51,58 and the stop-valve 60 in passage 34:, and by providing the by-pass61 connecting passage 3 1 with the exhaust, and the outlet pass 62, opening to the atmosphere upon opening its stop-valve 63, the vacuum piston 26 and the three-way valve may be rendered ineffective and may be omitted if desired. I 7 It will be noted that the proportional volumes of the main. and supplemental clearance chambers are determined by the particular characteristics of --the-engine, or other uniflow device to which my invention is applied. I

It will thus be observed that the engine or similar device constructed in accordance with my invention is adapted to operate under a great variety of industrial conditions in which it is desirable for flexibility and efficiency, as desired, to operate with exhaust or discharge pressures which may vary between .wide ilimits,say '26 inches vacuum and say 5 pounds gage back ,pressure for engines, etc. as will be understood by the art.

When my invention is employed .in combination with other types of units which operate on the uniflow principle, and which are not specifically defined .in detail herein above, my mventionis properly operated therewith by connection with either the suction line or the discharge line or both, or withany other suitable part of the uniflow unit, to effect-the desired variations or regulation of capacity and power required, and to attain the desired efficiency as may be determined by the particular circumstances.

From the above, it will be seen that I have devised a clearance means which positively effects the desired regulation of clearance value applicable to all types of units operating on the unifiow principle. I have also disclosed positivemeans for automatically attaining such desired regulation of clearance. I

Whereas I have described .my invention by reference to specific forms'thereof, it, will be understood that many changes and modi- With said source, said uniflow devicefcomprising a cylinder and a piston reciprocable within said cylinder and means for precluding compressional pressure within said cylinder in excess of said constant pressure, said precluding means including a clearance means comprising a plurality of clearance chambers, means for controlling the com munication of said clearance means with the interior of said cylinder and exhaust pressure responsive means controlling said controlling means.

' 2. The combination with a source of fluid compressed to a substantially constant pressure, ofva uniflow device communicating with said source, said uniflow device comprising-a cylinder and a piston reciprocable within said cylinder and means for precluding compressional pressure within said cylinder in excess of said constant pressure, said precluding means including a clearance means comprising a plurality of clearance chambers, and means for controlling the communication of said clearance chambers successively additively with the interiorxof said cylinder, said last-named means being responsive to variations ofthe exhaust fluid pressure.

3. The combination with a source of fluid compressed'to a substantially constant pressure, of a'uniflow device communicating with said source, said vuniflow device comprising a cylinder and a piston reciprocablewithin said cylinder and means for pre eluding compressional pressure within said cylinder in excess of said constant pressure, said precluding means including a clearance means comprising a plurality of clearance chambers,. and means for "controlling the communication of said clearance means suc- 'cessively additively and 'substractively with the interior of said cylinder, said lastnamed means being responsive to the variations of said exhaust fluid pressure. a

4. The combination with a source of fluid c mpressed to a substantially constant pressure, of a uniflow device communicating with said source, said'uniflow device compr sing a cylinder and a piston reciprocable within said cyl1n'der, and means ior'preeluding compressional pressure within'said cylinder in excess ofsaid constant pressure,

'said precluding means includinga clear ance means comprising main and supplementary clearance chambers, and means for controllingthecommunicationof said clearance chambers successively with the interior of said cylinder, saidlast-named means 'being responsive to variations of the exhaust fluid pressure. f j f g The combination 'with'asource' of compressed fluid, of a uniflow" device having its inlet communicating'with said source, said uniflow device comprising a :cylinder and a piston reciprocable within said cylinder and means for pre'cluding compressional pressure within the said'cylinder'in excess of the inflow fluid'pressure, said precluding means'including a plurality of clearance chambers, means for controlling, the 'communicationof said clearance chambers successively additively with the interior of said cylinder, and means responsive to variations of the exhaust fluid pressure and for controlling said communication controlling means] i i 6. The vcombination with'a source of fluid compressed to a substantially 'co'nstant'pressure, oi 1a uniflow device communicating with said source, said uniflow device comprising a cylind'er and apiston reciprocable .within saidcylinder and means for precluding compressional pressure within said cylinder in excess of said constant pressure, said" precluding means including a clearance fmeans' comprising clearance chambers-re spectively, I of different clearance values, means for controlling the communication of said clearance chambers successively additijvely and subtractivelywi'th theiinterior of said cylinder and means responsive to varia-,

tions of the exhaust fluid pressure;- for controlling said "communication controlling means.

7. The combination with a sourcetofc'ompressed fluid, of a uniflow device provided with a, cylinder, and a piston' reciprocable in"said cylinder, clearance meansfcomprisinga plurality of clearance elements, and

common means for controlling communication of said clearance elements successively with the interior of said cylinder, said com-.

,mon communication controlling means comprising a, device responsive to 5 variations of the-exhaust pressure and operating independently ofthe' speed of operation of the uniflow device. V

8. The combination'with a source ofc'om pressed fluid, of auniflow device and providedwith ya cylinder provided with inlet valves adj acent its opposite ends and an exhaust port disposedintermediate said cylinder ends and-*provide'dfurther with a pissaid last named 1' means {being re- 7 ton reciprocated in said cylinder,"clearance" -means comprlslng a plurality ofuclearance responsive to variations of the exhaust fluid prgssure for controlling said valve.

10. The combination with a source of compressed fluid, of a uniflow device provided with a cylinder provided. with inlet valves disposed adjacent its ends and an exhaust port disposed substantially centrally of said cylinder ends and provided further with a piston reciprocated in said cylinder, of clearance means comprising a main chamber, supplementalchambers and a piston valve control-lingthe' successive communication of said supplemental chambers with said main chamber and means responsive to variations of the exhaust fluid pressure and independently of the speed of operation of said uniflow device for controlling said valve. y r

.11. The combination with a pressure device employing a' compressible fluid and provided with a cylinder and apiston reciprocated in said cylinder, of clearance means comprising a main chamber, supplemental chambers communicating with said main chamber, a valve controlling the communication of said supplemental chambers with said main chamber and means responsive to the pressure at the exhaust region of the device controlling said valve.

12. The combination with a source of-compressed fluid, of a uniflow device and provided with a cylinder provided with an inlet, a piston reciprocated in said cylinder, an exhaust port controlled by said piston andmeans controlling said inlet, clearance means comprising a main chamber, supplement'al chambers respectively having ports opening into said main-chamber, a common valve controlling said ports and means responsive to variations of the exhaust pressure of said fluid for varying the position ofsaidvalve. l I

13'. The combination with'a source of compressed fluid of a uniflow device provided. witha cylinder and a piston reciprocated in; said: cylinder, clearance means comprising-ya plurality: ofclearance elements and means for cutting in and out successively said clearance elements, said last named means including means responsive to ling said inlet, a plurality of clearance chambers having spacially related ports, balanced valve means controlling said port's including means for balancing said valve at its different positions and means responsive to variations of the exhaust fluid pressure controlling said valve means. w

15. The combination with a source of com pressed fluid, of a uniflow device provided with a cylinder and a piston reciprocable therein, of a plurality of clearance CllELHlbers having spacially related ports, means for controlling said ports, a ditierential piston controlling said port controlling means and. means responsive to variations of the exhaust fluidpressure for controlling said differential piston.

16. The combination with a uniflow device employing a compressible fluid and pro.- vided with a cylinder and a piston reciprocable therein, said cylinder being provided with inlet and exhaust ports, of a plurality of clearance chambers having spacially related ports, a valve controlling saidports, a differential piston controlling said valve, fluid passage means leading to the effective surfaces of said differential piston and multiport means responsive to variations of. the exhaust fluid pressure for controlling said fluid passage means.

17. The combination. with a pressure device employing a compressible fluid? and provided with a cylinder and a piston reciprocable therein, of a plurality of'clearance chambers having spacially related, ports, a valve controlling said ports, a differential piston controlling said valve, passages leading to the eiiective surfaces of said difierential piston, multiport means controlling said passages and a plurality of balancing elements for said differential. valve.

18. The combination with a pressure devfice employing a compressible. fluid and provided with a cylinder anda' piston reciprocable thereimof a plurality of clearance chambers having spacially related ports, a'valve controlling said: ports, a difvferential piston controlling said valve, passagesleading to the efl'ective surfaces of said difl'erential piston, a plurality of weights and means for successively connecting said weights with said difl'erential piston. v a H -l9. The combination with, a: pressure device employing a compressible fluid and provided with a cylinder and a piston recipro- "mg to the effective surfaces of said cable therein, of a plurality of clearance chambers having spacially related ports, a

valve controlling said ports, a differential passages leaddifferential piston, a plurality of weights, and means for successively connecting and disconnecting said weights with and from said differential piston. I

20. The combination with a uniflow device having a cylinder, a piston reciprocable within said cylinder and a discharge outlet, of a clearance chamber, means controlling the communication of said chamber with said cylinder, a differential piston controlling said controlling means, a set of passages leading to the effective faces of said differential piston, a secondset of passages connected with said discharge outlet and the atmosphere, and a multiport valve for connecting and disconnecting said two sets of passages.

21. The combination with a source of compressed fluid, of a uniflow device provided with a cylinder and a piston reciprocated in said cylinder, clearance means comprising a plurality of clearance elements and fluid pressure balanced means for controlling the communication'of said clearance elements successively with the interior of said cylinder, said controlling means being responsive to variations of the exhaust pressure. 7

22. The combination with a source of compressed fluid, of a uniflow device provided with a cylinder and a piston reciprocated 1n said cylinder, clearance means comprising a plurality of clearance elements, fluid pressure balanced means for controlling the communication of said clearance elements successively with the interior of said cylinder, and means for operating said fluid pressure balanced means, said responsive to variations of the exhaust pressure.

23. The combination with a source of compressed fluid, of a uniflow device provided with a cylinder and a piston reciprocated in said cylinder, clearance means comprising a plurality of clearance elements, fluid pressure balanced means for controlling the communication of said clearance elements successively with the interior of said cylinder, and exhaust fluid pressure responsive means for operating said fluid pressure balanced means.

24. The combination with a source of compiston controlling said valve,

' by said piston,

operating means being pressed fluid, of a uniflow device provided 7 with a cylinder and a piston reciprocated in said cylinder, clearance means comprising a plurality of clearance elements, pressure balanced means for controlling the communication of said clearance elements successively with the interior of said cylinder, and means responsive to pressure variations in the exhaust of said cylinder for operating said pressure balanced means.

25. The combination of a source of steam supply of substantially constant pressure, of a'uniflow engine provided with a cylinder, an inlet for said cylinder,controlling means for said inlet, a piston reciprocable within, said cylinder and exhaust ports controlled of means for maintaining the compressional pressure within the said cylinder substantially equal to the initial pres sure, but precluding the rise of the compressional pressure in'exce'ss'of the initial pressure notwithstanding variations of the exhaust pressure, said compressional pres.- sure maintaining means comprising a plu-. rality' of clearance elements, fluid pressure balanced means for controlling the communication of said clearance elements successively with the interior of said cylinder and means for operating said fluid pressure balanced means in response to variations of the exhaust pressure and independently of the speed of operation of said uniflow engine. I

taining the compressional pressure within the-said cylinder substantially equal to the initial pressure but precluding-the rise of the compressional pressure in excess of the initial pressure notwithstanding variations of the exhaust pressure, said compressional pressure plurality of clearance elements, a .dlflerenmaintaining means comprising a tial piston controlling the communication of I said clearance elements with the interior of.

said cylinder and means controlling said dif- I ferential piston in response to variations of the exhaust pressure and independently of the speed ofoperationof saiduniflow engine. In testimony whereof I have signed this specification. i p

' EVERETT W. SWARTWOUT. 

